This invention relates to synthetic polyol ester lubricant base stocks, and more particularly to cross blends of high viscosity synthetic ester lubricant base stocks with conventional polyol ester base stocks suitable for use in compressor and refrigeration systems.
It is well known that chlorofluorocarbons previously utilized as propellants in aerosols and as refrigeration fluids are no longer used due to the adverse impact on the earth's ozone layer. Efforts to eliminate the use of chlorofluorocarbons have led to the development of alternative fluids that are highly or fully fluorinated hydrocarbons.
Working refrigeration fluids generally include a minor amount of lubricant. Typically, the refrigeration fluids include between about 5 to 15 or 20 parts by weight of lubricant with the balance being the fluorocarbon. In chlorofluorocarbon systems, lubricants were traditionally mineral oils which are fully miscible with the chlorofluorocarbons. However, such lubricants are not miscible with the highly or fully fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, commonly known as HFC-134a, and other chlorine-free fluorocarbons including hydrofluorocarbon (HFC) having 1 to 3 carbon atoms and preferably 1 to 2 carbon atoms, for example, difluoromethane (HFC-32), trifluoromethane (HFC-23), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-1 34), 1,1,1-trifluoroethane (HFC-1 43a), and 1,1-difluoroethane (HFC-152a).
Although HFCs are not miscible with mineral oil, certain carboxylic esters of polyhydroxy compounds, also known as polyol esters or POEs, are fully miscible with the highly or fully fluorinated fluids. The polyol ester lubricants are prepared by the condensation of certain polyols such as pentaerythritol, neopentyl glycol and trimethylpropanol, and linear or branched monocarboxylic acids containing between about 4 to 10 carbon atoms. To improve miscibility, the carboxylic acid mixture typically includes 30-85 mole % 3,5,5 tri-methylhexanoic acid (iso-C-9). However, recent events have limited the availability of iso-C-9. This shortage of iso-C-9 has made it difficult and/or expensive to manufacture polyol esters using iso-C-9.
Accordingly, it is desirable to provide synthetic ester lubricant base stocks miscible with HFCs having viscosities between about ISO 68 to 220 based on cross blends of two or more base stocks. The blend is comprised of a high viscosity synthetic base stock formed by condensation of neopentylpolyol and linear and branched monocarboxylic acids, wherein little or no iso-C-9 is used in the carboxylic acid mix, and a conventional polyol ester base stock. The cross blend is miscible with HFCs notwithstanding the limited use of isoC9, and provides an economical base stock in times where supplies of isoC9 are limited.